<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .outer{
            display: flex;
        }
        .box{
            margin-left: 20px;
            width: 300px;
            height: 200px;
            border: 1px solid black;
        }
        .box1{
            background-image: linear-gradient(red,yellow,green);
        }
    </style>
</head>
<body>
    <div class="outer">
        <div class="box box1"></div>
        <div class="box box2"></div>
        <div class="box box3"></div>
        <div class="box box4"></div>
        <div class="box box5"></div>
        <div class="box box6"></div>
    </div>
</body>
</html>